Microscopic particles such as a particular specie of bacteria lying in a fluid such as water or air, can be identified by detecting its pattern of light scatter when it passes through a light beam. A plurality of photodetectors detect light scattered in different directions from a light beam. Although a laser that generates the light beam and multiple photodetectors that detect scattered light can be immersed in a contaminated fluid, this has a disadvantage that the laser and photodetectors may be coated with a slime or other material in the fluid and may become contaminated so that they require decontamination before they are handled. A system which enabled detection and/or identification of microscopic particles by a light source such as a laser and by multiple photodetectors, which isolated the laser and photodetectors from the fluid, would be value. It would be desirable in many applications, if a considerable portion of the fluid was directed through the light beam rather than around it.
In accordance with one embodiment of the present invention, an apparatus is provided for detection and/or identification of microscopic particles in fluid by detecting light scattered by a particle as it passes through a light beam, which confines fluid flow to a path of small cross-section. The apparatus includes a solid transparent material such as glass having a passage through which fluid flows and having an outside surface where photodetectors are positioned. The passage has a flat front surface. This allows a passage of small cross-sectional area to be used while the photodetectors accurately detect light scattered from a particle lying in a small detect zone located along the light beam.